1. Part drawing analysis
The figure is the part drawing of the rear axle driven spiral bevel gear of a certain automobile. As shown in the figure, the spiral bevel gear is more complex than the ordinary gear because of the existence of the bevel angle and the spiral angle of the tooth shape, so the local material fluidity will be very poor in the forming process, and it is easy to have the situation that the local material flow is not smooth in the forming process, resulting in the mold cavity filling is not enough, so the processing and forming of the tooth shape area is the key and difficult point of the part manufacturing process. Because this project requires the near final forming of the gear, the part of the gear shape is as few as possible without subsequent machining and the forming quality is strict, so the part of the gear must be formed in the forging process. The key to the forming of the part is whether the tooth shape can fill the cavity of the tooth shape model satisfactorily and whether there are defects such as burr.
2. Determination of forging drawing of driven spiral bevel gear
2.1 determination of cold forging drawing
1). Determination of parting surface
The following factors are mainly considered in the determination of parting surface:
(1) The forging can be easily loaded and unloaded from the die bore;
(2) The metal can fill the mold well;
(3) Reduce the number of remaining blocks and the probability of burr;
(4) Reduce die forging process steps,
It is beneficial to simplify the mold manufacturing process. Through the above analysis, the maximum outer diameter of the spiral bevel gear is determined as the parting surface according to the structural characteristics of the spiral bevel gear.
2) . determination of forging dimensional tolerance and machining allowance
According to the technical roadmap in this paper, the tooth profile of the workpiece can be formed by casting process first, and then modified by closed hot die forging process. The final cold precision forging process can ensure that the dimensional accuracy and surface quality meet the requirements of the finished parts, so the tooth profile does not need machining, so there is no machining allowance. In consideration of the subsequent need to tap the threaded holes on the bottom of the gear, it is necessary to reserve a machining allowance of 1mm on the bottom of the gear according to the relevant process requirements. According to the contents of GB / T 12362-2003, the spiral bevel gear studied in this paper belongs to 4-level 4S complex forging, and the material coefficient is 1-level 1m, from which the dimensional tolerance of each part of forging can be obtained.
3) . die forging inclination
The tooth surface of the studied driven spiral bevel gear has a certain taper, that is, there is a natural die forging angle, so it can be easily taken out from the die without additional die forging angle. Through the above analysis, it is determined that the cold forging drawing of driven spiral bevel gear is as shown in the figure.
2.2 Determination of hot forging drawing
Based on the cold forging drawing, the size of the hot forging drawing is determined by considering the factors of material shrinkage and dimensional tolerance. Therefore, it is necessary to scale the cold forging drawing. The shrinkage of alloy steel forging is 1 ~ 1.5%. 20CrMoH is a low alloy steel, so the scaling factor is 1.012. The dimensional tolerance can be obtained by referring to GB / T 12362-2003.
Through the above analysis, it is determined that the hot forging drawing is as shown in the figure.